DESCRIPTION: The grant proposes to study immune reconstitution in HIV infected infants treated with HAART. The primary hypothesis tested is that children treated at an early age with maximum suppression of viral replication with have a greater potential for normalization of immune function than older patients. In addition, the authors will attempt to identify and quantify the cellular reservoirs for infectious and latent viral infection in HIV infected infants post-HAART and we will study HIV co-receptor use and tropism of latent virus which is found to be present post-HAART to infect thymocytes and macrophages will also be studied.